Motion blur is the visibly perceptible result of rapidly moving objects. This effect is seen as streaking or blurring in still images and in film, and is caused when the exposure time of a video camera is slow relative to an object's movement. In computer animation, however, exposure limitations are not present and moving images depicted in a scene are typically shown without motion blur. In order to depict motion blur in computer animations, computer animation systems apply motion blur techniques. For example, some motion blur techniques involve full-screen motion blur by determining a screen-space velocity, while others involve calculating velocity based on a camera's movement.
Techniques used for blurring computer animation are often limited by the capabilities of computer memory. Graphics processing units (GPUs) and software applications are required to share memory with other components, and in motion blur techniques, computer graphics are sampled several times in order to apply motion blur to animations, thus requiring a significant amount of memory.
In addition, computer processors are used by several computer applications that are in addition to software applying blurring techniques, and because these techniques require computer graphics to be repeatedly rendered, processors can be burdened by animation software requirements.
Memory and processor limitations aside, conventional computer graphic-based motion blur techniques are applied to objects moving linearly. FIG. 1A depicts samples 101, 102, 103, 104 taken of a moving object 100 along a linear direction, i.e., the objects' direction of movement, for generating a linear blur. For wheels rotating in computer animation, the wheel's movement is radial rather than linear. Applying blur techniques to objects not moving linearly do not depict realistic motion blurring. FIG. 1B depicts samples 101, 102, 103, 104 taken in a linear direction for a wheel 105 moving radially, resulting in samples taken from the background 110 as opposed to wheel 105. In addition, computer animated wheels rotating on a screen often stay in the same position on the screen, while the environment appears to move across the screen. As a result, realistically depicting rotating wheels with motion blur can be desirable for a viewer because the vehicle associated with the wheels and the wheels themselves may be viewed on the screen for a long period of time.
Some computer games centered around racing cars and motorcycles avoid sampling of rotating wheels and address some of the above problems by substituting detailed wheels with wheels having less detailed, streaky blurred wheels when wheels are to be depicted as rotating rapidly. However, for computer applications depicting animated wheels having a relief pattern such as knobs, substituting wheels with blurred texture is not a realistic substitute since the space between the knobs needs to be blurred and a texture cannot be applied to empty space. Accordingly, there is a need for motion blurring techniques to textured rotating objects having a relief pattern that do not overburden memory or processing capabilities.